Myth startup sequence

Most MythTV programs follow a common sequence:

1. Process (parse) command-line arguments
2. Create a MythContext object, which stores paths for later location of runtime assets (filters/fonts/plugins/themes/translations)
3. (optionally) Create a UPnP client or server
4. Initialise the MythContext, which:
   • Tries to find a database on localhost, or on the host specified in mysql.txt,
   • Tries to locate exactly one backend host via UPnP, to find its database,
   • If possible, displays a list of all backends located via UPnP for the user to choose from, or
   • Fails
5. Create the main window/screen, display themed menus, et c.

(examine program/*/main.cpp, and libs/libmyth/mythcontext.cpp, for further detail).

The "runtime assets" mentioned above are stored in a number of well-known locations. The following methods in MythContext allow programs and plugins to access these assets:

1. GetInstallPrefix() returns the value of MCP's m_installprefix variable, which is either the runtime env. var. $MYTHTVDIR or the compile-time var. RUNPREFIX. If these are relative paths, it is initialised relative to the binary location. The value is used thus:
   • GetInstallPrefix() + /share/mythtv/ = GetShareDir(), GetFontsDir()
   • GetInstallPrefix() + /share/mythtv/themes/ = GetThemesParentDir()
   • GetInstallPrefix() + /share/mythtv/i18n/ = GetTranslationsDir()
   • GetInstallPrefix() + /share/mythtv/mytharchive
   • GetInstallPrefix() + /share/mythtv/mytharchive/themes
   • GetInstallPrefix() + /share/mythtv/mytharchive/scripts
   • GetInstallPrefix() + /share/mythtv/mythflix/scripts
   • GetInstallPrefix() + /share/mythtv/mythnews
   • GetInstallPrefix() + /share/mythtv/mythvideo/scripts
   • GetInstallPrefix() + /share/mythtv/mythweather
   • GetInstallPrefix() + /share/mythtv/mythweather/scripts
   • GetInstallPrefix() + /bin/ignyte
   • GetInstallPrefix() + /bin/mythfilldatabase
   • GetInstallPrefix() + /bin/mtd
   • GetInstallPrefix() + /lib/mythtv/ = GetLibraryDir()
   • GetInstallPrefix() + /lib/mythtv/plugins/ = GetPluginsDir()
   • GetInstallPrefix() + /lib/mythtv/filters/ = GetFiltersDir()

2. GetConfDir() returns the value of the runtime env. var. $MYTHCONFDIR, or $HOME/.mythtv.

3. mysql.txt is loaded from GetShareDir(), GetInstallPrefix() + /etc/mythtv, GetConfDir(), and the current directory. Later files override the values from earlier ones.